This invention relates generally to inflatable-type modular occupant restraint systems for passenger vehicles. Such restraint are commonly know as air bags and may be installed in an automobile or other vehicle, at least in part on the steering wheel or adjacent to the driver for the protection of the driver and also in the dashboard or adjacent to an occupant for passenger protection in the event of a collision. More particularly, this invention relates to an improved means for controlling the discharge rate of gas from an air bag cushion and for preventing the over-pressurization of the air bag cushion.
Inflatable restraint systems for restraining the movement of occupants of a motor vehicle during a collision have long been known. The inflatable occupant restraint is located in close proximity to the occupant and is normally stowed in an uninflated condition. In the event of a crash, however, the inflatable occupant restraint is commonly designed to inflate with a gas in no more than a few milliseconds.
The inflation gas is normally produced or generated in or from a device referred to as a "gas generator" or, as it is more commonly known, an "inflator." In one common type of inflator, inflation gas is produced upon the ignition and burning of a gas generant material. The pressure of combustion gases resulting from the rapid burning of the gas generant material causes gas to rush into the bag to effect a rapid rate of inflation thereof.
An air bag cushion, which is normally made from a material that may be substantially impermeable to the flow of gas, typically is provided in part thereof with at least one vent port which serves as an outlet for gas contained within the air bag cushion. Alternatively, the air bag cushion may be provided in part thereof with a permeable fabric which functions as an outlet for gas contained within the cushion. The vent port or permeable fabric for typical operating conditions relieves excess pressure from within the air bag cushion to prevent the cushion from bursting and to prevent recoil of an occupant who impacts onto an over-pressurized air bag cushion. Increased venting to provide additional pressure relief for the air bag cushion may be desired in situations such as when: 1) the gas generating material of an inflator is more reactive due to being stored at a high temperature, e.g., such as being stored in a vehicle exposed to bright sunlight; 2) the vehicle is involved in a high-energy collision; or 3) when a relatively large occupant is to be subject to the action of the air bag cushion.
Prior solutions to the need for increased venting have used rupturable patches, seams or the like which break and open an exhaust vent to relieve excess pressure from within the air bag cushion. Such solutions are disclosed in Eyrainer et al., U.S. Pat. No. 5,219,179; Takada, U.S. Pat. No. 4,805,930; Okada et al., U.S. Pat. No. 4,097,065; Nakajima et al., U.S. Pat. No. 5,016,913; and Carey et al., U.S. Pat. No. 3,527,475.
As disclosed by Takada, stitched seams between fabric elements of an air bag cushion induce localized distension when the air bag cushion is exposed to excess pressure. The air bag cushion opens along the seams causing the film coating of the envelope fabric to rupture along the seams. This allows gas to escape and maintain a substantially constant overall maximum pressure, regardless of variation in ambient temperature.
In Okada, the air bag gas vent is covered with a gas-permeable cloth which is provided with at least one dart. When the dart tears, it provides a bulge-out portion to relieve pressure within the air bag cushion to prevent the cushion from bursting.
Heat-shrink material which partially blocks a gas vent is disclosed by Nakajima. The shrink-wrap shrinks to increase the area for the passage of gas from the air bag cushion when gas is introduced into the air bag cushion from the inflator.
A patch covering a gas vent is disclosed in Carey. The patch is made from material which has less strength than the material from which the air bag cushion is made. The patch is attached to the cushion with adhesive or similar means. When the air bag cushion is over-pressurized, the patch ruptures along the periphery of the gas vent forming a flap which moves to permit gas to exhaust from the air bag cushion.
In addition, there is a growing need and desire to employ inflatable restraints to provide protection to a vehicle occupant in the case where the vehicle is the subject of a side impact or collision. Side impact inflatable restraints, however, can present special demands or requirements on the inflatable restraint system.
For example, it is common for a side impact inflatable restraint to be stowed in positions (e.g., such as about the pillar beams of the vehicle or within the seat back cushion or door frame) that are in closer proximity to the occupant which is to be protected thereby, as compared to typical frontal impact inflatable restraints. Such closer storage typically will result in a reduction of the already short time interval between actuation of the inflatable restraint system and contact by the occupant with the inflated restraint. Thus, rapid inflation and proper venting are special concerns relative to side impact applications of inflatable restraints.